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2001 Microchip Technology Inc. DS39024B-page 67
SWITCH.C Description
8.6 SWITCH.C Source Code Listing
//****************************************************
//* SWITCH.C
//****************************************************
//* Rodger Richey
//* Principal Applications Engineer
//* Microchip Technology Incorporated
//****************************************************
//* 2 December 1998
//* Compiled using MPLAB C17 C Compiler V2.20
//****************************************************
//* This program toggles the state of the memory
//* mapped LEDs when the corresponding memory mapped
//* switch is pressed.
//****************************************************
//* Uses an oscillator of 16MHz
//****************************************************
#include <p17c756.h>
#include <delays.h>
void main(void)
{
unsigned int LEDbuf;
unsigned int SWTbuf;
unsigned int TEMPbuf;
unsigned int Temp;
rom int *LEDptr;
rom int *SWTptr;
// Initialize pointers to the memory mapped device
LEDptr = (rom int *)0xfffd;
SWTptr = (rom int *)0xfffc;
// Initialize the LEDs and other variables
*LEDptr = 0x00ff;
LEDbuf = 0x00ff;
SWTbuf = 0x00ff;
while(1)
{
// Read the state of the switches
TEMPbuf = *SWTptr & 0x00ff;
// Determine what switch states have changed
Temp = TEMPbuf ^ SWTbuf;
// If a switch state has changed and the change
// was a switch press
if(Temp && TEMPbuf != 0x00ff)
{
// If need to toggle LED low
if(Temp&LEDbuf)
// Mask off desired
LED
LEDbuf &= ~Temp;
// Else need to toggle LED high